REPRESENTATIVE GEOPHYSICAL SERVICES

1. Surface Ground-Penetrating Radar---(Dipole-Dipole Radar)

Method: A very short-pulse electromagnetic signal is coupled into the earth
by means of a specially designed antenna. The reflected signals are detected
by a second antenna and time delays of the various radar reflections from
sub-surface targets are measured on an RF oscilloscope. Oscilloscope
Polaroid photography of radar A-scope output. Frequencies used are
typically between 20 and 150 MHz depending on the application. New high
power design achieves a transmitted power of 30 kilowatts. Not destructive
or harmful to the environment in any way. The equipment is small and light
weight and easy to use underground. Very useful in confined spaces, or in
vertical mountings for viewing through a wall or hillside, or in other
situations where a cart radar can not be used. Radar can be monostatically or
bistatically mounted. Very good distance resolving power. Does not
generate RFI or electrical interference. Battery powered if AC power not
convenient.

Measures distance in the earth to cavities, pipes, or other dielectric
discontinuities

Ranges to 300 feet in favorable locations

Easy to use in confined spaces or underground

Depth to bedrock below fill in some situations

Allows point by point mapping of subsurface anomalies from different
viewing angles

Limitations: Not suitable in high clay or some types of moist soils where
radio-frequency attenuation is extremely high. Low angular resolution typical
of dipole antennas. May suffer from clutter limitations typical of all types of
ground-penetrating radar in certain environments.

2. Cart-Mounted Ground-Penetrating Radar (GPR)

Method: A very short-pulse electromagnetic signal is coupled into the earth
by means of a specially designed antenna. The reflected signals are detected
by a second antenna equipped with a high-gain built in preamplifier. The
antennas and associated electronics are mounted on a wheeled-cart for ease
in traversing large areas of the surface. (Ski mounting of radar is available
for use on sand or ice and snow surfaces). Frequency used is typically 150
MHz. Radar output processed by a personal computer and a false-color
display is used. Output is recorded on video tape or hard disk with voice
comments and cart-position information. Color print outs of the data are
available. Very good distance resolving power. Does not generate RFI or
electrical interference. Battery operated when AC power is inconvenient.

Useful in radar mapping large areas of the sub-surface in a highly
efficient manner.

Limitations: Not suitable in high clay or some types of moist soils where
radio-frequency attenuation is extremely high. Low angular resolution typical
of dipole antennas.

3. Borehole Ground-Penetrating Radar (GPR)

Method: A very short-pulse electromagnetic signal is coupled into the earth
by means of a specially designed antenna axially mounted in a four-inch
diameter cylinder. The reflected signals are detected by a second cylindrical
borehole antenna equipped with a high-gain built in preamplifier. The
antennas can be lowered up by means of RF cable reels to 400 feet deep in
borehole. Radar output is displayed on oscilloscope screen for A-scope
photographing. Antennas can be used in monostatic or bistatic
configuration. Very good distance resolving power. Does not generate RFI
or electrical interference. Battery operated when AC power is inconvenient.
Transmitter generates 30 kilowatts peak power which is a factor of 30 times
higher than any known GPR now on the market. The frequency used is 150
MHz.

Bistatic or monostatic capability

Useful ranges to 500 feet borehole to borehole

RF cables allow useful depths to 400 feet in boreholes

30 Kilowatts transmitter power

Excellent Signal-to-Noise levels are readily attainable

Limitations: Not suitable in high clay or some types of moist soils where
radio-frequency attenuation is extremely high. Low angular resolution typical
of dipole antennas.

4. High Frequency Seismics And Concrete Thickness

In the past there has been no easy way to measure the thickness of concrete
slabs or footings. Has the contractor poured to meet specs or is the slab
only attaining the correct thickness at one or two points? Are the footings
under my building as deep as they should be? Why has my slab cracked?

Similar question often arise regarding concrete foundational piers. Are the
concrete piers under my house as deep as shown on the blueprints? Were
they poured all at once or on subsequent days? Have piers cracked or been
broken since they were installed?

What is the depth of soil over bedrock and how competent is the bedrock?

A unique, one-of-a-kind High Frequency Seismic Sounder can often
provide answers about concrete thickness and depth not obtainable any
other way except by direct excavation.

High Frequency Seismic Sounding is a new geophysical method which can
be very helpful when probing into concrete or solid rock. (The method is
not suitable for direct probing into soil since compressional seismic waves
are difficult to generate into soils). Two seismic transducers are employed.
A transmitted pulse is introduced into the concrete through one of these
transducers and the second unit is used as a receiver. A thin film of water-soluble gel is used at the transducer-concrete interface to achieve the
necessary coupling for sound waves in and out of the medium. A short
pulse up to several hundred watts in intensity is used. The frequency chosen
is normally between 1000 and 30,000 Hz (1-30 kHz).

Since the velocity of propagation of sound waves in concrete is accurately
known, the time delay of reflected signals is measured from an oscilloscope
display. The results yield the thickness of concrete slabs, foundation depths
or pier depths. Cracks and fractures in concrete piers frequently show up on
the HF Seismic Sounder. In some situations the sounder can measure
depths of fill over bedrock under a concrete slab. Voids and cavities under a
slab are usually detectable.

In order to successful sound into concrete the seismic transducers need to be
emplaced directly over the area to be examined. In the case of piers or
footings one can usually probe through wooden headers and beams
provided they are in good mechanical contact with the concrete beneath. The
sounder can also be used for viewing horizontally into concrete. In this case
the transducers are pressed tightly against the concrete and clamped in place
to assure intimate contact.

Most surveys using the High Frequency Seismic Sounder can be completed
in one working day with results available immediately at the site.

Top: CW: Cart Radars in use on ice and on city street, Portable radar in use in wet underground tunnels.
Bottom: CW: Superstition Mountains, Philippines, Philippines, Borehole radar at Victorio Peak, WSMR, New Mexico.